1. Field of the Invention
The present invention broadly relates to gas turbine rotors and, more particularly, is concerned with a retainer construction for locking turbine rotor blades in the periphery of a turbine rotor disc and for sealing coolant passageways within the disc.
2. Description of the Prior Art
In a gas turbine engine, turbine blades are typically attached to a rotor disc by inserting them in axially-directed slots formed in the rim of the disc. The blades are usually held in place by a thin circular plate called a blade retainer which is attached to either or both sides of the disc by suitable fastening means such as conventional bolts. Examples of such a blade retainer are represented by the one-piece prior art designs illustrated in FIGS. 1 and 2.
In addition to holding the blades in stationary positions on the rotor disc, the retainer commonly serves two additional functions. First, it seals a cavity between the blades and the rotor disc to allow cooling air to flow to the blades with minimal leakage to the external environment. Second, it dampens vibration of the blades as a result of an axial load imparted into the blades at an area below the airfoil of each blade.
In certain high pressure turbines, these blade retainer designs have proven unacceptable for applications where long cyclic lives are required, in that, they are low cycle fatigue limited in the bolt hole region. In addition, they typically impart large loads into the rotating discs and create cyclic life problems in the disc itself. Consequently, a need exists for a blade retainer design which effectively reduces the high stresses encountered in both the disc and the retainer itself, and thereby greatly improves component cyclic life.